Where did the function "V" define?

[DuskSwan]

I notice a function 'V' when defined method copy of class ModifiableModule, but cannot find what it mean, nor where it defined. So what it is? I will be grateful for anyone's directions!

↓ the V in code

    def copy(self, other, same_var=False):
        for name, param in other.named_params():
            if not same_var:
                param = V(param.data.clone(), requires_grad=True)
            self.set_param(name, param)

[DuskSwan]

well, i find it at the start from torch.autograd import Variable as V